find missing time periods

[Office User]

Need to find gaps in a series of time periods (ie 8-8:30, 8:30-9. I have a
table with the time periods and a query that groups the dates and times for
each worker. The Unmatched query won't work because the worker may have only
been "clocked out" from 8-9 on 9/1 but from 10-11 on 9/2.

Any help you can give will be greatly appreciated. Here's the SQL for the
unmatched query I attempted.

SELECT [Time Periods].Period, [Time Periods].[Start Time]
FROM [Time Periods] LEFT JOIN [Grouped by Date & Time] ON [Time
Periods].[Start Time] = [Grouped by Date & Time].Login
WHERE ((([Grouped by Date & Time].Login) Is Null));


Thanks,
Marcia